Reconstructions of temperature variations from Antarctic ice cores rely on the assumption that the relationship between hydrogen and oxygen isotope ratios and temperature are stable in space and time.
Links:
[1] http://admin.indiaenvironmentportal.org.in/feature-article/evidence-warmer-interglacials-east-antarctic-ice-cores
[2] http://admin.indiaenvironmentportal.org.in/category/author/l-c-sime
[3] http://admin.indiaenvironmentportal.org.in/category/author/e-w-wolff
[4] http://admin.indiaenvironmentportal.org.in/category/author/k-i-c-oliver-et-al
[5] http://admin.indiaenvironmentportal.org.in/category/journal/nature
[6] http://admin.indiaenvironmentportal.org.in/category/thesaurus/climate-change
[7] http://admin.indiaenvironmentportal.org.in/category/thesaurus/climate-science
[8] http://admin.indiaenvironmentportal.org.in/category/thesaurus/antarctica